This invention relates to ultrasound systems in general and, more particularly, to systems and methods for improving the beamforming quality in ultrasound array imaging.
Ultrasound is an increasingly common tool for viewing the internal body matter, such as organs or tissue, of a patient in real time. In an ultrasonic imaging system, acoustic signals are transmitted from a transducer into the patient. A portion of the acoustic signals are reflected by the body matter to create echoes that are received and interpreted to produce an image of the patient""s body. In this interpretation process, beamformers are utilized to focus the received echo signals along a receive beam line. The resulting focused echo signals are used by a scan converter to form the image on a display.
Two important factors to consider in producing a quality image are the lateral and contrast resolution of the image. The lateral and contrast resolution are both directly dependent on the performance of a particular beamformer used in the ultrasonic imaging system. A point spread function in the lateral dimension is often used to illustrate how the lateral and contrast resolution of an image are affected by the use of the particular beamformer under a given geometry. A point spread function measures the intensity of a point target being imaged at each lateral dimension for a particular depth of the image field.
In general, the lateral resolution of an image is determined by the width of a main beam of a point spread function corresponding to the image, while the contrast resolution is dominated by sidelobe levels of the point spread function. The best lateral resolution is achieved by a sharp, main beamwidth. The best contrast resolution occurs when sidelobe levels are low. Unfortunately, one is often achieved at the cost of the other. For example, when a beamformer utilizes a boxcar apodization, the main beamwidth produced in the corresponding point spread function is sharp, but the sidelobe levels are high. In contrast, when a beamformer utilizes a hamming window apodization, the sidelobe levels produced in the corresponding point spread function are reduced at the cost of a wider beamwidth. As a result, for conventional ultrasound array imaging, lateral resolution and contrast resolution are generally not optimized at the same time.
Therefore, there is a need for an ultrasound array imaging system in which the beamwidth and sidelobe levels are optimized such that lateral and contrast resolution of an ultrasonic image are simultaneously enhanced.
In accordance with this invention, an ultrasound array imaging system and method for improving beamforming quality and ultimately for improving an ultrasound image are provided. In one embodiment of the invention, the ultrasound array imaging system includes a transducer, a first beamformer, a second beamformer and a comparator. The first beamformer receives electronic echo signals from the transducer and produces a first apodized beam signal in accordance with a first beamforming apodization. The second beamformer receives the same electronic echo signals from the transducer and produces a second apodized beam signal in accordance with a second beamforming apodization. The first and second apodized beam signals are compared in the comparator which then produces a combined, apodized beam signal for output to a scan converter for creating an improved ultrasound image.
In accordance with other aspects of this invention, the ultrasound array imaging system further includes a first amplitude detector for receiving the first apodized beam signal and a second amplitude detector for receiving the second apodized beam signal. The amplitude detectors produce amplitude detected, first and second apodized beam signals. The amplitude detected, first apodized beam signal represents the amplitudes of a number of points along a particular receive beamline used by the transducer to collect the original data as calculated using the first beamformer, while the amplitude detected, second apodized beam signal represents the amplitudes of the same points on the same receive beamline as calculated by the second beamformer.
The comparator receives the amplitude detected, first and second apodized beam signals and selects the data from the particular apodized beam signal that has the minimum value for that particular point. The selected minimum amplitude data is used to produce a single combined apodized beam signal for the particular receive beamline. This entire process is repeated for each receive beamline along which data is collected by the transducer.
In accordance with further aspects of this invention, the ultrasound array imaging system described above can function with multiple beamformers, each having a different apodization function, for producing multiple apodized beam signals. These multiple apodized beam signals can be similarly compared and combined by the comparator to produce a single combined apodized beam signal for transmission to a scan converter for creating an image on a display monitor.
In accordance with yet further aspects of this invention, instead of comparing first and second apodized beam signals produced using either a single beamformer programmed to calculate data in accordance with different apodizations or two separate beamformers each calculating data according to a different apodization, the ultrasound array imaging system can produce first and second sets of echo data that are created in response to a first and a second transmit pulse having a first and a second apodization respectively. In this embodiment, the first and second sets of echo data are produced using the same receive beamformer implementing a single receive apodization.